Illinois Child Support Calculator

An estimator for how child support is calculated in Illinois using the Income Shares model.

What is the Illinois Income Shares Model?

Since 2017, Illinois has used the “Income Shares” model to determine child support obligations. This marks a significant shift from the old method, which was based on a flat percentage of the non-custodial parent’s income. The core idea behind the Income Shares model is that a child should receive the same proportion of parental income that they would have received if the parents had not divorced and were still living together.

This modern approach combines both parents’ net incomes to arrive at a total amount of money that should be dedicated to the child’s care. That total obligation is then divided between the parents based on their proportional share of the combined income. This system is designed to be more equitable by considering the financial situation of both parents. For information on related topics, you might want to read about {related_keywords}.

The Formula for How Child Support is Calculated in Illinois

The calculation for child support in Illinois follows a specific, multi-step process defined by statute. While our calculator automates this, understanding the formula is key. There are two primary calculation paths depending on parenting time.

Standard Parenting Time Calculation (< 146 Overnights)

1. Determine Each Parent’s Net Income: Gross income from all sources is calculated, and then standardized deductions (like taxes) are taken out to find the monthly net income for each parent.
2. Combine Net Incomes: The two net incomes are added together to get the Combined Monthly Net Income.
3. Find the Basic Support Obligation: The state of Illinois provides an official “Income Shares Schedule” which is a large table that cross-references the Combined Monthly Net Income with the number of children to find the Basic Child Support Obligation. This figure represents what a typical family at that income level spends on their children.
4. Calculate Income Percentages: Each parent’s individual net income is divided by the combined net income to find their percentage share. (e.g., Parent A earns 60%, Parent B earns 40%).
5. Determine the Final Obligation: The Basic Support Obligation is multiplied by the paying parent’s (the one with less parenting time) income percentage. This result is the amount they pay to the other parent.

Shared Parenting Time Calculation (≥ 146 Overnights)

When each parent has the child for at least 146 overnights per year (about 40% of the time), the state recognizes that both parents are incurring significant direct costs for the child. The formula becomes more complex:

1. Follow steps 1-3 above to find the Basic Support Obligation.
2. Calculate the Shared Care Obligation: The Basic Support Obligation is multiplied by 1.5 (150%). This accounts for the duplicated costs of maintaining two separate households for the child (e.g., two bedrooms, two sets of clothes, etc.).
3. Prorate by Income Share: This new, larger Shared Care Obligation is allocated between the parents based on their percentage of the combined income.
4. Prorate by Parenting Time: Each parent’s individual obligation is then multiplied by the percentage of time the *other* parent has the child.
5. Offset and Finalize: The two resulting amounts are offset. The parent with the higher obligation pays the difference to the parent with the lower obligation.

Variables Table

Key variables in the Illinois child support calculation.

Variable	Meaning	Unit	Typical Range
Net Income	Each parent’s monthly income after taxes	USD ($)	$1,000 – $20,000+
Number of Children	The number of minor children shared by the parents	Count	1 – 6+
Parenting Time	Number of overnights per year the child spends with a parent	Overnights (Days)	0 – 365
Basic Support Obligation	State-determined cost to raise children at a specific combined income level	USD ($)	Varies by income/children

Practical Examples

Example 1: Standard Parenting Time

• Inputs:
  • Parent 1 (Payor) Net Income: $4,000/mo
  • Parent 2 (Recipient) Net Income: $2,000/mo
  • Number of Children: 1
  • Parent 1 Overnights: 100 per year
• Calculation:
  1. Combined Net Income: $4,000 + $2,000 = $6,000
  2. Basic Support Obligation (from IL schedule for $6k income, 1 child): Approx. $1,215
  3. Parent 1 Income Share: $4,000 / $6,000 = 66.7%
  4. Result: Parent 1 pays 66.7% of $1,215 = $810.41 per month to Parent 2.

Example 2: Shared Parenting Time

• Inputs:
  • Parent 1 Net Income: $6,000/mo
  • Parent 2 Net Income: $4,000/mo
  • Number of Children: 2
  • Parent 1 Overnights: 150 per year (Parent 2 has 215)
• Calculation:
  1. Combined Net Income: $6,000 + $4,000 = $10,000
  2. Basic Obligation (for $10k income, 2 children): Approx. $2,159
  3. Shared Care Obligation: $2,159 * 1.5 = $3,238.50
  4. Parent 1 Share ($6k/$10k = 60%): $3,238.50 * 0.60 = $1,943.10
  5. Parent 2 Share ($4k/$10k = 40%): $3,238.50 * 0.40 = $1,295.40
  6. Parent 1 Obligation (prorated by P2 time): $1,943.10 * (215/365) = $1,145.42
  7. Parent 2 Obligation (prorated by P1 time): $1,295.40 * (150/365) = $532.36
  8. Result: Parent 1 pays the difference: $1,145.42 – $532.36 = $613.06 per month to Parent 2.

For more detailed calculations, you can explore {related_keywords}.

How to Use This Illinois Child Support Calculator

Our tool is designed to provide a reliable estimate based on the information you provide. Here’s how to get the most accurate result:

1. Enter Net Incomes: Input the monthly take-home pay for both Parent 1 and Parent 2. This should be your income after federal/state taxes and FICA have been deducted.
2. Select Number of Children: Use the dropdown to choose how many minor children are covered by this support order.
3. Enter Parenting Time: Provide the number of overnights the children spend with Parent 1 annually. The calculator will automatically determine if the 146-night shared parenting threshold is met and apply the correct formula.
4. Review the Results: The calculator instantly updates, showing you the estimated monthly payment, who pays whom, and key values used in the calculation like the combined income and basic obligation.

Key Factors That Affect How Child Support is Calculated in Illinois

While the calculator covers the core formula, several other factors can influence the final court-ordered amount. Understanding these is crucial for anyone wondering how is child support calculated in Illinois.

• Gross vs. Net Income: The calculation is based on net income. The state provides specific conversion charts to standardize this, but disputes can arise over what qualifies as income or a valid deduction.
• Parenting Time (The 146-Night Cliff): As shown, crossing the 146-overnight threshold dramatically changes the formula. Accurately counting overnights is one of the most critical aspects.
• Health Insurance & Childcare Costs: The cost of the child’s health insurance premium and necessary work-related childcare can be added to the basic obligation, increasing the total support amount before it’s allocated.
• Spousal Maintenance (Alimony): If one parent pays or receives spousal maintenance from the other, this can be added or subtracted from their income before calculating child support.
• Extraordinary Expenses: Costs for special medical needs, therapies, or agreed-upon extracurricular activities can be ordered by the court to be shared by the parents in addition to basic child support.
• Imputed Income: If a court believes a parent is voluntarily unemployed or underemployed to avoid paying support, it can “impute” income to them—calculating support based on what they *should* be earning.

Learning about {related_keywords} can provide further insight.

Frequently Asked Questions (FAQ)

1. Does the mother’s income affect child support in Illinois?

Yes, absolutely. Under the Income Shares model, both parents’ incomes are a fundamental part of the calculation. The court combines both net incomes to determine the total support obligation.

2. Is child support in Illinois based on gross or net income?

It is based on net income. Illinois law provides a standardized gross-to-net income conversion chart that is used to ensure fairness and consistency in calculations.

3. What happens if both parents have 50/50 custody?

If each parent has the child for an equal number of overnights (e.g., 182.5), this is well over the 146-night threshold for shared parenting. The shared parenting formula will be used. Unless both parents have the exact same net income, one parent will still likely pay child support to the other to equalize the child’s standard of living between the two homes.

4. Does a new law mean there is no more interest on back child support?

Yes, a recent change in Illinois law eliminated the accrual of statutory interest on past-due child support payments. However, this does not forgive the original debt. The full amount of missed payments is still due and can be aggressively enforced by the state.

5. Can a parent refuse visitation if child support is not paid?

No. In Illinois, parenting time (visitation) and child support are treated as separate legal issues. A parent cannot legally withhold court-ordered parenting time because the other parent is behind on support payments.

6. What is the difference between the old law and the new law?

The old law (pre-2017) used a simple percentage of the non-custodial parent’s net income (e.g., 20% for one child). The new “Income Shares” law considers both parents’ incomes, making it a more balanced model.

7. What if one parent has no income?

If a parent is genuinely unable to work due to disability, their income may be calculated as zero. However, if a court finds a parent is voluntarily unemployed, it may impute income to them based on their earning potential and calculate support based on that higher figure.

8. How are daycare and health insurance costs handled?

These are typically considered “add-on” expenses. The monthly cost for the child’s health insurance premium and work-related daycare are often added to the basic support obligation and shared between the parents based on their percentage of the combined income.